Box girder

ABSTRACT

A composite structure comprises a box girder with concrete cast onto a surface thereof, the box girder being provided with at least one elongate strengthening member which extends upon the said surface and projects into the concrete, shear loads being transmitted from the concrete to the box girder via the strengthening member.

United States Patent Needham July 15, 1975 [54] BOX GIRDER 1.791.881 2/1931 Yarwood 52/336 1.858.512 5/1932 Lan enber 52/725 1 1 Fredemk Harold Needham 1 863.258 6/1932 rasii ianf 52/336 England 2.731.824 1/1956 Hadley 52/334 3.027.687 4/1962 Baroni 52/334 [73] Asslgnee. grltishdsteel Corporation. London. 3.257.764 6/1966 Gripe I I I I I I U 52/724 3.624.980 12/1971 McManus 52/334 22 Filed; June 25 1974 3.736.716 6/1973 Nishimura 52/334 [21] Appl. No.: 483,019

Primary Eruminer-Henry C. Sutherland Related Apphcanon Data Attorney. Agent. or Firm-Bacon & Thomas [63] Continuation of Ser. No. 310.977. Nov. 30. 1972.

abandoned.

[30] Foreign Application Priority Data [57] ABSTRACT 1971 United Kingdom 56384/71 A composite structure comprises a box girder with concrete cast onto a surface thereof. the box girder U-S. being provided with at least one elongate trengthen- [51] Int. Cl E041 /1 041 5/18: E046 3/3 ing member which extends upon the said surface and Fleld of Search projects into the oncrete. shea loads being transmit- 53/724- 731 ted from the concrete to the box girder via the strengthening member. [56] References Cited UNITED STATES PATENTS 3 Claims, 6 Drawing Figures 770.983 9/1904 Rediich 52/724 PATENTEDJUL 1 i975 153,894,378

F/G.7. 2 r12 PRIOR ART 2% FIGS. 35 (37 BOX GIRDER This is a continuation of now abandoned application Ser. No. 310,977, filed Nov. 30, 1972.

This invention relates to improvements in box girders and to composite structures including box girders.

In one aspect, the invention provides a composite structure comprising a box girder with concrete cast onto a surface thereof, the box girder being provided with at least one elongate strengthening member which extends upon the said surface and projects into the concrete, shear loads being transmitted from the concrete to the box girder via the strengthening member.

The said surface may be the upper external surface of the box girder, the strengthening member extending longitudinally thereof.

Alternatively or in addition, the said surface may be an internal surface of the girder, particularly the bottom internal surface of the girder or an internal surface of an end box of the girder.

In another aspect the invention provides a box girder strengthened by at least one elongate strengthening member disposed on and projecting from an external surface of the box girder and extending longitudinally thereof, whereby when concrete is cast over the said external surface, shear loads between the concrete and the box girder are transmitted via the at least one strengthening member.

In one embodiment of the invention, the said external surface is the upper external surface.

In a further aspect, the invention provides a box girder having an open-topped end box, an internal side surface of the end box having at least one elongate strengthening member extending downwardly upon said surface and projecting into'the box whereby when concrete is cast into the end box as part ofa composite structure including the box girder, shear loads are transmitted between the concrete and the end box via the at least one strengthening member.

The shear loads may be transmitted by adhesion of the concrete to the strengthening member, and/or by mechanical interaction between the concrete and the member.

Preferably the strengthening member has sidewaysextending portions adapted to engage the concrete and prevent it separating from the box girder.

The strengthening member may be a rolled section.

The box girder may be provided with one or more internal diaphragms.

There may be means to reduce bearing stresses at a region where the strengthening member passes over a said diaphragm.

The invention will be described merely by way of example with reference to the accompanying drawings, wherein: I

FIG. 1 is a cross section through a composite structure including a conventional box girder,

FIG. 2 is a broken-away section on line 2-2 of FIG.

FIG. 3 is a cross section through a composite structure including a box girder according to the invention,

FIG. 4 is a broken-away section on line 44 of FIG. 3, and

FIGS. 5 and 6 are sections through further composite structures according to the invention.

Referring to FIGS. 1 and 2, a conventional composite structure comprises a rectangular-section steel box girder 10 which is provided at intervals along its length with diaphragms 12, one of which is shown in FIG. 2. The box girder also is provided with longitudinally extending strengthening members 14, the diaphragms being slotted at 16 to permit the passage of the strengthening members.

A layer of concrete 18 is cast upon the upper external surface 20 of the box girder and is connected thereto by means of a large number of shear studs 22. It will be seen from FIGS. 1 and 2 that the shear studs are distributed both sideways and longitudinally on the box girder. The function of the sheer studs 24 is to transmit shear loads between the concrete 22 and the box girder 10. These shear loads normally act longitudinally of the girder, as indicated by arrows 26 in FIG. 2. The shear studs transmit these shear loads by the generation of thecompressive stresses between the concrete and the surfaces of the shear studs which are perpendicular to the direction of the shear loads. The heads of the studs 24 also prevent separation of the concrete 22 from the box girder.

This conventional box girder and composite structure suffers from certain disadvantages. Firstly, the shear studs normally are welded to the box girder in a fabrication shop and are prone to damage erection of the girder. Also, a girder having a large number of shear studs on its upper surface presents a hazardous surface for workmen to walk on. Another disadvantage is that the slots in the diaphragms 12 weaken them, making it necessary to use heavier gauge material, or to more generously dimension the diaphragms, or to employ more diaphragms more closely spaced.

The embodiment of the present invention illustrated in F105. 3 and 4 provides a box girder and composite structure in which these problems are avoided.

Referring to FIGS. 3 and 4 a box girder 30 is provided with longitudinal strengthening members 32 on its external upper surface. No longitudinal strengthening members are provided internally of the girder. A layerof concrete 34 is cast upon the upper external surface of the box girder 30, enclosing the strengthening members 32.

The strengthening members 32 extend longitudinally of the box girder, and therefore present relatively large longitudinally extending side surfaces 36. The concrete 34 adheres only weakly to the surfaces 36 of the strengthening members 32, but due to the relatively large area of the surfaces this adhesion is sufficient to transmit shear loads (again indicated by arrows 26) between the concrete 34 and the box girder. If the shear loads are particularly large, the strengthening members may be provided with sideways-protruding lugs, or may hav'e holes in their flanges, so that there is a mechanical (as opposed to merely adhesive) interaction between the concrete and the members 32 for transmission of shear loads. Transverse reinforcing rods may be passed through the holes. Thus the use of shear studs and the problems associated with them are avoided.

The strengthening members 32 are shown as bulb flats, but can equally well be other rolled sections e.g. flats, angle-sections, T-sections, I-sections or troughsections. Sections such as angle-sections, T-sections and bulb flats have the added advantage that they have sideways-extending portions (e.g. the bulbs 37 of the bulb flats) which engage the concrete 34 similarly to the heads of shear studs and prevent it separating from the box girder.

Clearly, by placing the strengthening members 32 exa ternally of thebox girder, the members 38 may be made narrower because they do not have to be slotted.

Similarly .panel diaphragms may be made of thinner r gauge material. Thus, two items, the conventional shear studs and internal stiffeners, are replaced by a single item: the external stiffeners 32. e y

In orderto,reduce excessive bearing stresses in the areas 40.of the. diaphragms38 where thestiffeners 3 2 pass oyer them, gusset plates 39 (FIG. 4) are attached to the diaphragms directly beneath the stiffeners. These gusset plates are triangular and are welded both to the diaphragms and to the underside of the upper surface of the girder. Then the bearing stress applied to each diaphragm is spread also over the area of the top of the gusset plate, instead of being transmitted only via the small area .40. Gusset plates 39 maybe employed with either picture-frame or panel typev diaphragms.

It will be appreciated that whilst it is preferable to provide strengthening members 32 only on an external surface of the box girder, they can also be provided internally as well if necessary. Then it is necessary to provide slots in the-diaphragms, but the use of shear studs still may be avoided. r

FIG. 5. illustrates afurther embodiment of the inventionl There is shown a cross-section through a box girder 41 wherein a composite structure is formed by casting concrete 42 inside the box girder. The box girder is provided with longitudinally extending strengthening members 44 on its bottom internal surface..These members are as described with reference to FIGS. 3 and 4, and they transmit shear between the concrete and the box girder in the same'way. Thus, the use of shear studs is avoided.

FIG. 6 shows a longitudinalsection through a composite structure in which the invention is employed to anchor concrete in the end box of a box girder 5 0. The box girder 50 has an o pentopped end box 51 having a bottom define'd by the bottom flange of the girder 50 and sides defined by the webs of the girder 50, by an end plate 52 and by a diaphragm Concrete 56 is cast over the box girder as in;the FIG. 3 embodiment, and also fills the box 51. Strengthening members 58 extend verticallydownwardly ,upon the inner surfaces of the end plate 52- and the diaphragm 54 to preventbuckling. Shear loads between the concrete in the box 51 and thegirder 50 are transmitted via the strengthening members 58. Thetransmission may be by adhesion or by mechanical interaction aspreviously described with zreferenceto FIGS. 3 and 4. External stiffeners 60 also ,may be provided on the top surface of the girder 50 as described with reference to those figures. 7

ln,addition to the invention defined in the following claims, the present application also is directed to any other novel feature or combination. of features herein disclosed and/or shown in the drawings I claim: I

1 A box girder. having an open-topped end box and adapted to have concrete. cast over itstop surface, and into theend box, comprising: a bottom wall, a pair of side walls, an outer end wall fixed to. saidbottom, and side walls, an inner end wall spaced from said outer end wall andforming aside wall of the open-topped end box, a top wall termi natingat one end adjacent said inner end wall, at least one flanged stiffening member fixed to and upstanding from the external surface .of said top wall, said stiffening member extending along the length of said top wall and being substantially longitudinally aligned with the longitudinal .axisof the box girder, at:least one stress bearing diaphragm mounted within the box girder and extending transversely thereof, and at least onenelongate strengthening memher fixed to and extending downwardly upon an internal side surface of said open-toppedend box, whereby ,when concrete is cast onto the external surface of said tween the concrete and the box girder.

2. A structure as claimed in claim 1 includin g strengthening means fixed to said diaphragm and to the internal surface of said top wall to reduce bearing stress at positions where the longitudinal stiffening means overlies said diaphragm. 

1. A box girder having an open-topped end box and adapted to have concrete cast over its top surface and into the end box, comprising: a bottom wall, a pair of side walls, an outer end wall fixed to said bottom and side walls, an inner end wall spaced from said outer end wall and forming a side wall of the open-topped end box, a top wall terminating at one end adjacent said inner end wall, at least one flanged stiffening member fixed to and upstanding from the external surface of said top wall, said stiffening member extending along the length of said top wall and being substantially longitudinally aligned with the longitudinal axis of the box girder, at least one stress bearing diaphragm mounted within the box girder and extending transversely thereof, and at least one elongate strengthening member fixed to and extending downwardly upon an internal side surface of said open-topped end box, whereby when concrete is cast onto the external surface of said top wall and into the end box to form a composite structure with the box girder, the stiffening member and thE strengthening member transmit shear loads between the concrete and the box girder.
 2. A structure as claimed in claim 1 including strengthening means fixed to said diaphragm and to the internal surface of said top wall to reduce bearing stress at positions where the longitudinal stiffening means overlies said diaphragm.
 3. A structure as claimed in claim 1 wherein the flange of said flanged stiffening member is a bulbous member. 